I don't have anything against them, but don't approve of some applications of them. Just like real guns.
Water guns, Nerf guns, guns with sticky darts, and airsoft guns have been around for a long time, and they are fun. Purely fun. They need to be handled carefully, because even a low power airsoft gun can injure, and people have been killed using Super Soaker type water guns.
Today's usage, I think, focuses best on target games. When I was a kid, the emphasis with toy guns was with war games. The difference is probably because of the recent memory of WW2, and the then current Viet Nam war. As with other cultures at war (notably Japan between the 1890s and WW2), toy stores were stocked with mock armaments so that kids would be used to using weapons.
We have no similar situation today. The landscape is different, and one of the disturbing applications of toy guns today is the "shooter" video game, which depict the player has hunting down and shooting a victim. I disappprove of games like that.
As for paint ball, I think it's a children's war game played by people who are old enough to have grown past that stage in life.